With advances in digital video technologies, so-called 3D display technology, which causes display images to be seen as three-dimensional, is becoming popular.
Such 3D display technology is being adopted primarily in television display devices and personal computers, but the possibility exists of broadly applying this to all devices accompanied by display screens (for example, digital photo frames and/or the like).
Methods for realizing 3D displays primarily include those (glasses type) that cause a 3D display to be recognized using display assistance devices such as special eyeglasses that a viewer wears to look at the display screen, and those (naked eye type) that cause a 3D display to be recognized with the naked eye without using this kind of display assistance device.
In television display devices and the like, the glasses type 3D display system is widely used.
For example, in Unexamined Japanese Patent Application KOKAI Publication No. 2010-62767, a shutter system called a time division system such as so-called frame sequential system is disclosed as a method for realizing a higher quality glasses-type 3D display.
This system is one in which display devices alternately displaying images for the right eye and images for the left eye are synchronized and a liquid crystal shutter and/or the like is incorporated into the lens portion of the glasses and operates so that images for the right eye reach only the right eye and images for the left eye reach only the left eye.
Particularly in television display devices, such glasses-type approaches are more suitable than naked eye types due to the fact that there are no restrictions on viewing position, and moreover, from an image quality viewpoint, such time-division systems are suitable because there is no deterioration of spatial resolution.
Because right-eye images and left-eye images are images shifted in the left-right direction in accordance with binocular parallax in the horizontal direction when video is shot, viewing such video as a 3D display requires the viewer to view with a posture such that the horizontal direction of the display screen and the left-right direction of the viewer's eyes are in the same direction within a prescribed range (hereafter referred to as “normal viewing range”).
That is to say, because the posture of the viewer relative to the display screen must be fixed within a prescribed range, this has the inconvenience that there is little freedom in the viewer's posture.
Furthermore, when the direction of the binocular parallax in the video and the left-right direction of the viewer diverge due to viewing in a posture that is not in the normal viewing range, not only are the images not seen as a 3D display, but due to continuously viewing unnaturally shifted images, so there are concerns of negative physiological effects could occur, such as visual strain or eyestrain.
In addition, the object that is to be viewed three-dimensionally when viewing a 3D display is not actually shown as a three-dimensional object but is recognized three-dimensionally in the brain due to binocular parallax, so viewing as a 3D display is accomplished through a physiological stereopsis function.
Formation of the stereopsis function through binocular parallax is said to be completed by around age 5-6, so there are concerns that negative physiological effects could arise, when an infant in which formation of the stereopsis function is immature, or an elderly person in which the stereopsis function has degraded, views a 3D display.
Hence, a method is desired for effectively preventing individuals with these conditions from viewing a 3D display.
In consideration of the foregoing, it is an object of the present invention to provide a display system, display device and display assistance device with which a 3D display can be appropriately viewed.